Field of the Invention
The present invention relates to a wireless communication system, and more particularly, to a method for changing, by a UE, priority in a wireless communication system, and an apparatus for supporting the same.
Related Art
3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) that is an advancement of UMTS (Universal Mobile Telecommunication System) is being introduced with 3GPP release 8. In 3GPP LTE, OFDMA (orthogonal frequency division multiple access) is used for downlink, and SC-FDMA (single carrier-frequency division multiple access) is used for uplink. The 3GPP LTE adopts MIMO (multiple input multiple output) having maximum four antennas. Recently, a discussion of 3GPP LTE-A (LTE-Advanced) which is the evolution of the 3GPP LTE is in progress.
In recent years, there is growing interest in a Device-to-Device (D2D) technology performing direct communication between devices. In particular, the D2D is attracting attention as a communication technology for a public safety network. A commercial communication network has been rapidly changed to the LTE but a current public safety network is based on a 2G technology in a collision problem and a cost side with an existing communication standard. Request for the technology clearance and an improved service induces an effort to improve the public safety network.
The public safety network has high service requirements (reliability and security) as compared with a commercial communication network. In particular, when coverage of cellular communication is insufficient or is not used, there is a need for direct signal transmission/reception between devices, that is, a D2D operation.
The D2D operation may be signal transmission/reception between adjacent devices to have various advantages. For example, a D2D UE may perform data communication with a high transmission rate and low delay. Further, the D2D operation may distribute traffic converged in a base station. If the D2D UE serves as a relay, the D2D UE may serve to extend coverage of a base station.
The 3GPP has created a working group exclusively responsible for Public Safety LTE (PS-LTE), TSG Service and System Aspect (SA) WG6 (hereinafter, “SA6”), in December 2014 to work for PS-LTE that is an issue of increasing concern around the world in recent years. SA6 is undertaking the standardization work for defining the structure of applications layers of functional items of the Mission Critical Push To Talk over LTE (MCPTT) standard for public safety and for specifying functions thereof.
An MCPTT service may be broadly divided into an on-network service operating within the coverage of a network and an off-network service operating outside the coverage of the network. Requirements for the on-network service include group settings and group call settings, a one-to-many calling method, a one-to-one calling method and call control, and a group control function. A requirement for the off-network service includes a function for direct device-to-device communication